There is one major difference - in a 401k you have a minimum retirement distribution (MRD) from 70 1/2 years of age onwards.
This means regardless of if you need the money or not, you will have to take a certain portion out.

In a Roth-IRA your funds can grow as long as they want (including past your living) without having to take out a single dollar, so you can potentially have them grow for a longer time and can take out exactly what you need, not what you have to take out.